Poppet valves are used in a wide variety of applications, such as for controlling the exhausting of hydraulic fluid from cylinders, motors and other working elements. Fluid flow from an inlet port through the poppet valve to an outlet port thereof is typically controlled by controllably moving the poppet between a closed position in sealed relation to a seat and a range of open positions displaced from the seat. A basic type of poppet valve has at least one throttling slot through the poppet to communicate the pressure in the inlet port to a control chamber at the backside of the poppet. The fluid pressure in the control chamber exerts a closing force on the poppet holding it against the seat. A spring is also generally used to hold the poppet against the seat when the pressure conditions in the inlet port, control chamber, and an outlet port, are equalized.
Controls for operably controlling the opening of the poppet are well known. Such known controls typically operate by regulating communication between the control chamber and another location such as the outlet port of the poppet through a variable regulating or flow control orifice under control of a pilot fluid signal, a solenoid, or the like. The variable regulating or flow control orifice is normally closed so that fluid pressure in the control chamber equals the inlet pressure and the poppet is urged against the seat by the pressure in the control chamber. Opening of the poppet is achieved by controllably opening the variable regulating or flow control orifice to communicate the control chamber with the outlet port or other location. This creates a pressure drop through the throttling slot in the poppet such that the inlet pressure urges the poppet from the seat as the control pressure drops below the balance pressure. The degree of opening of the poppet is subsequently controlled by controlling the flow through the variable regulating or flow control orifice to regulate the balance condition and the flow through the throttling slot.
Commonly, some leakage of fluid is expected to occur through the control apparatus, and a fluid drain to tank is typically provided for draining such leakage. However, in certain applications, for instance wherein the poppet is used as a load control device, such leakage is a problem as it can make it difficult for the poppet to be maintained in a balanced condition, resulting in load drift, that is, movement of the actuator or other working element controlling the load.
Additionally, there are certain disadvantages to allowing the leakage to be removed via a separate drain to tank. Such disadvantages include that the poppet becomes less controllable as the pressure drop from load pressure to the drain across the control is generally not the same as the pressure drop across the poppet valve. The poppet valve also becomes sensitive to down stream pressure (back pressure) and can become destabilized at high back pressure, that is, it can go to a fully open position and fail to respond to control inputs. Also, when flow is allowed to drain to tank, voiding problems can arise during regeneration operation involving a hydraulic cylinder circuit operating under an overrunning load. Further, back pressure is often introduced into the line to tank in order to address the voiding problem when operating with overrunning loads. However, addition of back pressure has been found to destabilize the poppet.
Accordingly, the present invention is directed to overcoming one or more of the problems as set forth above.